The age-related, T-independent immunologic properties limit the effectiveness of polysaccharides, including capsular polysaccharides and detoxifies lipopolysaccharides of invasive bacteria, as vaccines in infants and in immunocompromised adults. Synthetic schemes to covalently bind polysaccharides to proteins have been devised to increase the immunogenicity of the polysaccharides and to confer T-cell dependent immunologic properties upon these protective antigens. Based upon our work and the work that followed, Haemophilus influenzae type b conjugate vaccines have been licensed by the Food and Drug Administration for routine immunization of infants. There are several conjugate vaccines, two are currently licensed for use in infants, in the United States. The serum antibody response induced by PRP-T (a vaccine fashioned directly after our research) was studied in Charlotte, North Carolina. The technology of binding polysaccharides to proteins has been extended also to poly alpha(2->8) NeuNAc (the capsular polysaccharide of group B meningococcus Escherichia coli K1, Pasteurella haemolytica serotype A2). A cross-reactive E. coli polysaccharide K92, elicited antibodies to this and to the related poly alpha(2->9) NeuNAc (group C meningococcus capsule). This technology has also been extended to the polysaccharides of Cryptococcus neoformans, Staphylococcus aureus and the detoxified lipopolysaccharides of Shigella. The phase 1 studies with these latter products have been completed successfully.